This invention relates in general to the field of electro-optics and, more particularly, to a method and system for manufacturing a photocathode.
There are numerous methods and systems for detecting radiation. In one type of detector, photocathodes are used in conjunction with microchannel plates (MCPs) to detect low levels of electromagnetic radiation. Photocathodes emit electrons in response to exposure to photons. The electrons can then be accelerated by electrostatic fields toward a microchannel plate. A microchannel plate is typically manufactured from lead glass and has a multitude of channels, each one operable to produce cascades of secondary electrons in response to incident electrons. A receiving device then receives the secondary electrons and sends out a signal responsive to the electrons. Since the number of electrons emitted from the microchannel plate is much larger than the number of incident electrons, the signal produced by the device is stronger than it would have been without the microchannel plate.
One example of the use of a photocathode with a microchannel plate is an image intensifier tube. The image intensifier tube is used in night vision devices to amplify low light levels so that the user can see even in very dark conditions. In the image intensifier tube, a photocathode produces electrons in response to photons from an image. The electrons are then accelerated to the microchannel plate, which produces secondary emission electrons in response. The secondary emission electrons are received at a phosphor screen or, alternatively, a charge coupled device (CCD), thus producing a representation of the original image.
Another example of a device that uses a photocathode with a microchannel plate is a scintillation counter used to detect particles. High-energy particles pass through a scintillating material, thereby generating photons. Depending on the type of material used and the energy of the particles, these photons can be small in number. A photocathode in conjunction with a microchannel plate can be used to amplify the photon signal in similar fashion to an image intensifier tube. The detector can thus be used to detect faint particle signals and to transmit a signal to a device, e.g., a counter, that records the particle""s presence.
The photocathode may include one or more layers of material deposited or grown on a surface of the photocathode to provide anti-reflection properties, filtering properties, electron transportability properties, and other suitable properties associated with the photocathode. After the layers have been deposited or grown on the surface of the photocathode, the layers generally require selective etching to reduce the layer to a thickness to provide the desired photocathode properties. For example, etch solutions such as hydrochloric acid may be applied to the layer for a predetermined time period to reduce the thickness of the layer a required amount.
Various fixtures may be used to retain the photocathode during the etching process. For example, one such fixture that has been used in the past includes a cylindrical housing having openings at each end. A first end of the housing defines a passage for directing an etch compound to an etch surface of the photocathode. The etch surface of the photocathode may be seated against an angled seating surface of the housing. The fixture may also include a base to threadably engage the housing and apply a force to the photocathode to seal the etch surface of the photocathode against the angled seating surface and align the etch surface of the photocathode with the passage of the housing. The base may also have a recess formed in an end thereof to receive the photocathode and help align the etch surface with the passage of the housing.
However, prior systems and methods for manufacturing a photocathode suffer several disadvantages. For example, misalignment of the etch surface of the photocathode with the passage of the insert may result in the etch compound flowing beyond the etch surface of the photocathode. Additionally, the base may not adequately secure the photocathode against the insert, thereby allowing the etch compound to travel beyond the etch surface of the photocathode. As a result, the etch compound may cause material removal from adjacent portions of the photocathode and/or may cause subsequent photocathode material processing difficulties.
Accordingly, a need has arisen for a better technique having greater flexibility and adaptability for manufacturing a photocathode. In accordance with the present invention, a system and method for manufacturing a photocathode is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods.
According to one embodiment of the present invention, a system for manufacturing a photocathode includes a cap comprising a first end and a second end. The first end defines a passage operable to direct an etch compound to an etch surface of the photocathode. The system also includes a support operable to releasably engage the cap to align the etch surface of the photocathode with the passage of the cap. The system further includes a plunger operable to extend through a passage in the support to secure the photocathode against the cap to confine the etch compound to the etch surface of the photocathode.
According to another embodiment of the present invention, a method for manufacturing a photocathode includes positioning the photocathode on a support such that an etch surface of the photocathode faces away from the support. The method includes inserting an end of the support containing the photocathode into a cap. The cap comprises a passage operable to direct an etch compound to the etch surface of the photocathode. The method also includes aligning the etch surface of the photocathode with the passage of the cap using the support. The method also includes inserting a plunger through a passage in the support to contact a surface of the photocathode opposite the etch surface of the photocathode. The method further includes securing the photocathode against the cap using the plunger to confine the etch compound to the etch surface of the photocathode.
The technical advantages of the present invention include providing a system for manufacturing a photocathode that provides increased reliability during an etch process of the photocathode. For example, according to one aspect of the present invention, the base includes a seating area to align the etch surface of the photocathode with the passage of the insert to prevent misalignment of the photocathode during the etch process.
Another technical advantage of the present invention includes increased seal integrity between the photocathode and the insert. For example, according to one aspect of the present invention, a plunger extends through a passage in the base to secure the photocathode against the insert. The plunger includes a greater moment arm to exert an increased pressure against the photocathode to seal the photocathode against the insert, thereby preventing the etch compound from traveling beyond the etch surface of the photocathode.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.